1. Field of the Invention
This invention relates to an information processing system and, more particularly, to a system having a function of transferring data blocks from a memory unit to another unit according to an access request.
2. Description of the Prior Art
Many existing computer systems have dynamic random access memories (DRAMs) as a memory device. DRAMs have a large capacity but are comparatively low in access speed. To reduce the influence of this drawback upon a computer system, various means, e.g., using a cache memory, have been devised. A cache memory is a memory for storing data combined into blocks with addresses. Ordinarily, these blocks are controlled with respect to a unit corresponding to an integer multiple of an access band width of the memory. In the case of data loading in the cache memory from the DRAM when a mis-hit occurs, data blocks are transferred by continuously accessing data corresponding to an integer multiple of the memory access band. Under access control of a conventional memory controller, the operation of the block transfer function of the DRAM is executed at the time of such data block loading in the cache memory.
In this conventional system, however, the operation of the block transfer function of the DRAM is not executed unless a kind of access clearly stated as access to data with continuous addresses, i.e., a block access, is designated. Block access or ordinary access is determined according to whether the access target belongs to a cacheable address area or an uncacheable address area. Generally, data which needs to be accessed at a high speed is placed in a cacheable area while data which need not be accessed at a comparatively high speed is placed in an uncacheable area. There is a locality of address reference patterns in a program, which is called a locality of reference. This is true with respect to both cacheable and uncacheable areas. Presently, an increase in the speed of access to data belonging to a cacheable area is achieved by using a high-speed cache memory, but no speedup means has been provided for accessing data belonging to an uncacheable area.